This invention relates to an improved apparatus for exposing photosensitive media.
Known print-making devices include a rectangular glass plate with a light source on one side and a door or curtain on the other side. Means are provided for drawing a vacuum between the door or curtain and the glass plate. This vacuum is drawn after an original film to be copied ("a negative or positive") and an overlying sheet of material containing a photosensitive layer (e.g. diazo) are positioned on the glass plate. The vacuum flattens the sheets against the plate. A light source is turned on in order to expose the photosensitive layer. The exposed photosensitive sheet is thereafter developed.
In U.S. Pat Nos. 4,526,463 and 4,707,124, incorporated herein by reference in their entireties, a curtain is rolled across the sheets and plate with the vacuum being drawn as the curtain advances. Also, the plate, as shown in these patents, may be inclined with a roller mechanically pressing the curtain against the sheets and plate.
In such prior devices, the support structure for the glass plate has been found to be unsatisfactory. More particularly, because the underside of the glass plate is normally exposed to the light source, structural support for the glass plate is typically not provided within its interior portions. Support systems for such glass plates have provided support along each of the four edges of the glass plate. As a result of such a configuration, the glass plate sags in its middle portion. This sagging presents an area or gap wherein air can be trapped between the original film and sensitized media. Unless the media is drawn tightly against the glass plate, prints with blurred areas can be produced. Although these gaps can be eliminated by drawing a vacuum for a long period of time (i.e. five minutes or more), this slows down the print making process.
Therefore, an improved glass support apparatus is required to overcome these and other problems of the prior art.